This book concentrates on the design of individual parts, that is detail design, leading to the design of machines to meet a statistically quantified requirement of reliability. This area has been neglected by most reliability texts to date, even though it is the basis of all mechanical reliability. Owing to its impact on whole life costs, reliability has increasingly become an essential part of any machine specification, so nowadays design for quantified reliability can no longer be ignored. Here the author shows for the first time that even when material properties are expressed statistically there are some aspects (for example, strain hardening) that are fundamentally deterministic. This allows a design methodology to be formulated which is not too dissimilar from contemporary methods based on factors of safety and so on, although these do not allow reliability to be quantified and so must be replaced Changing from contemporary methods to one that achieves a quantified statistical reliability should therefore not be too difficult. While full use is made of statistical reliability concepts, crucial fundamental aspects are critically reviewed before use. In fact it emerges that surprisingly little statistics is needed to formulate a design methodology to achieve a quantified reliability, although more discussion of materials science aspects is required. Throughout, the guiding principle has been to consider practical design. The steps in the design methodology are given in detail and possible difficulties of implementation are discussed. Reference is also made to the economic optimization of a design. Finally, a general design strategy which ensures a reliable product is formulated.